The present invention relates to image pickup devices using image sensors such as CCDs (Charge Coupled Devices) and, more specially, to the image pickup devices that obtain both of still and motion images.
Conventional image pickup devices, which process photoelectricity conversion by image sensors such as CCDs and create digital picture signals having a specified format by digital signal processing, can be classified to video cameras picking up motion images and digital still cameras picking up still images. Cameras being able to pick up both of still and motion images are also proposed. Such cameras are disclosed in U.S. Pat. No. 5,170,249 and Japan Photograph Institute Fine Image Symposium 1995, pp. 59–62, “Development of Compact Digital Camera” for example.
In the above prior art, the image sensors generally are for motion images, that is, CCDs for the video cameras. The example of the color filter array used for such image sensors is shown to FIG. 3A. In this example, the complementary color filter of MG (magenta), G (green), CY (cyan) and YE (yellow) are used.
The signal of two pixels that adjoin in the vertical direction are mixed and outputted in case of generating a motion image data by using an image sensor with these color filters.
And, the video signals in the analog TV (television) signal standards such as the NTSC system are interlace signals. In such systems, quasi interlace scanning, which changes combinations of lines to be mixed for generating the interlace signals, are done.
Also, In case of taking a still image picture with this image sensor, the signals of pixels that adjoin in the vertical direction are not mixed, and the signals of each pixel are read independently. In this case, the pixel signals of odd number lines are read on the first field, the pixel signals of even number lines are read on the first field, and the still image are generated by sequentially converting the signals of the first field and the second field.
On the other hand, the image sensors that have large number of pixels than those of conventional video cameras are proposed for higher resolution of the still images. The numbers of the pixels in the vertical direction of these image sensors are larger than the number of scanning lines of the present television system. For example, in case the number of the effective pixels in the vertical direction is 960, it becomes the double of the number of the scanning lines in the television system. The example of the color filter arrangement of this image sensor for a still image is shown in FIG. 3C. In this filter, the RGB of the three elementary colors are used.
But there is a problem that when the number of pixels of a CCD is increased for the higher resolution, the formation of a motion image becomes difficult.
For example, in case using the CCD that has 250,000 pixels comprising 500 pixels in the vertical direction and 500 pixels in the horizontal direction, the CCD can output 30 flame images per second by the driving frequency of about 10 MHz, and a motion image such as by the NTSC system are made at real time. However, when the number of pixels in the horizontal and the vertical directions on the CCD becomes double for the higher resolution, the total number of the pixels of the CCD becomes 4 times. For example, in case that the number of the pixels in the vertical direction of CCD is 960, it is necessary to output the signals of 240 lines per one field by extracting one pixel from four pixels. Such process causes aliasings and deteriorates images.